832 BIOLOGICAL EFFECTS OF RADIATION 



was more than three times as intense as that in b, the leaves were thicker 

 in b, and sHghtly better differentiated; they were also shghtly superior 

 to those in the minus violet house (mv) which had nearly the same light 

 intensity as fs and vs. However, for leaves, the last mentioned were 

 superior to all of the colored lights and showed very nearly the same 

 conditions as the cross sections of the leaves of outdoor plants. 



Plants exposed to the "visible spectrum" (vs) showed greater diam- 

 eter and height of stem than was found in control plants growing out-of- 

 doors, but the outdoor plants showed greater vascular development 

 than the former. It appears that minus violet (mv) caused better 

 vascular development than blue (6) or red (r). Leaf development, as 

 shown by the thickness of the sections and tissue differentiation in the 

 leaf was greater in b than mv and least in r, while root development was 

 very similar to leaf development with mv superior to b. 



The comparisons of the total cross-sectional area of the stem in 

 terms of the stele, following the method of Priestley (26), are not given 

 by Pfeiffer. (See also New Phytologist 21: 60-61. 1922.) However, 

 from a study of the photomicrographs of the cross sections of soy bean 

 and sunflower stems which are shown in the plates (using sectors in many 

 cases and estimating the cross-sectional areas of the whole stem compared 

 with the stelar area) one finds an indication of the same general conditions 

 as in Priestley's etiolated stems. Whether only the full-spectrum and 

 visible-spectrum houses are used as standards of comparison, or the 

 out-of-door plants are included in the standard, makes little difference. 

 The stelar areas are not so well developed in any of the houses with 

 colored lights of reduced intensity, but in this analysis the blue seems to 

 result in stem structure which compares very favorably with the minus 

 violet and red lights of many times greater intensity. 



In an investigation embracing 43 experiments with liverworts, ferns, 

 and flowering plants, Teodoresco (38) used white light and two colored 

 lights: red-orange and blue-violet. Double-walled bell glasses filled 

 with 7-cm. layers of 10 per cent potassium bichromate solution were 

 used as filters for orange-red light, and similar bells filled with 3.2 to 

 4.25 per cent ammoniacal hydrated copper sulfate solution served as 

 filters for the blue-violet. The energy content of the transmitted light 

 was measured by means of a thermocouple and adjusted to comparable 

 conditions of intensity under these filters by diluting or concentrating 

 the liquid of the filter and by supplementing the illumination by electric 

 light. Plants well supplied with reserve foods were selected for most of 

 the tests and the experiments terminated before the supply of reserves 

 was entirely exhausted. The tubers, bulbs, and seeds of higher plants 

 were planted in sand, some older plants in pots, while the spores of lower 

 plants were planted in 2 to 5 per cent agar containing Ko of the standard 



